1. Field of the Invention
The invention relates in general to an integrated services digital broadcasting terrestrial (ISDB-T) reception system, and more particularly to a deinterleaving technique in an ISDB-T reception system.
2. Description of the Related Art
As communication technologies progress, developments of digital television broadcasting have also matured. In addition to cable wires, digital television signals may also be transmitted as wireless signals through equipments such as base stations or satellites. Integrated services digital broadcasting terrestrial (ISDB-T) and digital terrestrial multimedia broadcast (DTMB) are currently two prominent standards in the field of digital television broadcasting. Such standards adopt a transmission technique based on orthogonal frequency-division multiplexing (OFDM) modulation. OFDM modulation is a multi-carrier modulation, which disperses data to many orthogonal sub-carriers in different frequencies in a way that each of the sub-carriers can transmit data at a lower bit transmission rate. A length of inverse fast Fourier transform (IFFT) that generates OFDM signals can be categorized into various modes, each of which corresponds to different carrier lengths and different numbers of delay frames.
To counteract noise interference and multipath distortion during a transmission process, an ISDB-T transmission end and a DTMB transmission end performs time-interleaving and frequency-interleaving on data to be transmitted. Correspondingly, reception ends of the two systems need to perform a convolutional deinterleaving procedure on received data in order to correctly restore the original data. A convolutional deinterleaver, according to a known deinterleaving rule, respectively stores data transmitted by different carriers to a memory (usually a dynamic random access memory (DRAM) or a static random access memory (SRAM)). By appropriately designating storage positions (i.e., selecting correct data/buffer corresponding relations) and arranging delay time periods, the data later sent out from the memory become data having undergone the deinterleaving procedure.
In current techniques, in one set of data, apart from an in-phase component and a quadrature component, a channel state indicator (CSI) corresponding to the set of data is also stored into the memory by the convolutional deinterleaver. The channel state indicator represents channel quality at the time when the reception end including the deinterleaver receives the set of data, and is critical information for subsequently generating an input signal for a Viterbi decoder.
Taking an ISDB-T system for example, each OFDM symbol transmitted to a reception end includes 27960*13 sets of data. Assuming that each set of data and its channel state indicator require a storage space of 20 bits, the above memory for the convolutional deinterleaver is at least in a size of several megabytes (MB). Therefore, the memory capacity required by a convolutional deinterleaver is formidable, and thus constitutes a considerable part in hardware costs of a reception end.